Styrenic block copolymers (SBCs), most notably those of DuPont's Kraton® family, such as styrene-butadiene type polymers (e.g., styrene-butadiene di-block, SB; styrene-butadiene-styrene tri-block, SBS), have historically served the asphalt and footwear industries for years, with markets also in the industries of packaging, pressure sensitive adhesives, packaging materials, etc. Of these markets, the use of SBSs as bitumen modifiers is one of the largest and the most forgiving in terms of material properties.
The global asphalt market is to reach 118.4 million metric tons by 2015, according to a January 2011 report by Global Industry Analysts, Inc. The asphalt paving industry accounts for the largest end-use market segment of asphalt. With increasing growth in the developing markets of China, India, and Eastern Europe, asphalt will be increasingly needed to construct roadway infrastructure for the next decade. The increased demand for asphalt, along with the need for improved asphalt materials/pavement performance, creates the opportunity for an asphalt modifier.
The grade of the asphalt governs the performance of paving mixtures at in-service temperatures. In many cases, the characteristics of bitumen needs to be altered to improve its elastic recovery/ductility at low temperatures for sufficient cracking resistance as well as to increase its shearing resistance for sustained loads and/or at high temperatures for rutting resistance. The physical properties of bitumen are typically modified with the addition of SBS polymers to produce an improved asphalt grade that enhances the performance of asphalt paving mixtures. Of the asphalt mixtures that are polymer modified, approximately 80% of polymer modified asphalt uses SBS-type polymers.
Over the past few years, the price of butadiene, the principal component of SBC polymers used for bitumen modification, has increased dramatically. In 2008, there was a shortage of SBS polymers for the asphalt industry. With the forecast of increasing demand of liquid asphalt for the next decade, there remains a strong need for a new type of cost-effective, environment-friendly, viable polymers that can be used as an asphalt modifier in lieu of standard styrene-butadiene type modifiers.
Vegetable oils have been considered as monomeric feedstocks for the plastics industry for over 20 years. Polymers from vegetable oils have obtained increasing attention as public policy makers and corporations alike have been interested in replacing traditional petrochemical feedstocks due to their environmental and economic impact. To date, moderate success has been achieved through the application of traditional cationic and free radical polymerization routes to vegetable oils to yield thermoset plastics (i.e., plastics which, once synthesized, permanently retain their shape and are not subject to further processing). While these thermoset materials may indeed supplant a number of petrochemically-derived thermosets, the vast majority of commodity polymers are highly processable thermoplastic materials. There is thus a need in the art to develop from vegetable oils a highly processable thermoplastic and elastomeric polymer with a wide range of applications and physical properties.
The present invention is directed to fulfilling these needs in the art.